Influence of Molecule Size on Its Transport Properties through a Porous Medium

Abstract

The mass transfer kinetics of toluene and polystyrenes (of which the M(w) varies from 162 to 1.85 x 10(6) g mol(-1)) through columns filled with silica porous spheres were studied by inverse size exclusion chromatography. The mass transfer parameters were measured by modeling the band broadening of the chromatograms. The experimental height equivalent to a theoretical plate (HETP) data were analyzed using the general rate model in order to determine the effective diffusion coefficient in porous particles as a function of molecular size. The bulk molecular diffusion coefficients were experimentally determined by dynamic light scattering (DLS) and Taylor dispersion analysis (TDA). The topological tortuosity of the porous particles was determined by electrical measurements. The effective molecular diffusion coefficient through porous particles was modeled taking into account exclusion, friction, and at last tortuosity effects. A phenomenological law is proposed to model the evolution of the tortuosity experienced by a molecule in a porous particle as a function of its size. It gives a good prediction of the evolution of effective diffusion coefficient with the molecule/pore size ratio.

The obstruction factor in size-exclusion chromatography. 1. The intraparticle obstruction factor

“…As such, we used this constant offset between each set of plots, in combination with Eq. (9), to obtain the D m in THF of PMMA with M < 30,000 g/mol (applying a similar procedure to PS < 30,000 g/mol yielded D m that very closely matched those measured by Wernert et al in reference [27]). …”

“…For PS in THF, D m were Table 1 Intraparticle obstruction factor ( p ) values for PS and PMMA at both 30 and 50 • C for a 8 m particle size, 10 4Å pore size column. obtained from [27]:…”

Tortuosity of mesoporous alumina catalyst supports: Influence of the pore network organization

“…To the best of our knowledge, Inverse Liquid Chromatography (ILC) to study mesoporous alumina supports has never been reported in the literature so far. Nevertheless, the use of ILC to characterize transport properties of large molecule in silica has already been reported [5] .…”

Numerical Simulation of Hindered Diffusion inγ-Alumina Catalyst Supports

“…The tortuosity factor as function of accessible pore volume fraction is plotted in Figure 14, compared with an experimental reference by Inverse Size Exclusion Chromatography (ISEC) with p = 2.4 [5] plotted in blue dotted curve.…”

“…Its applicability has been experimentally assessed by permeability [9], electrical conductivity [11] or effective diffusion [5] measurements. Hindered diffusion coefficient in nanoporous solids can be measured by proton Pulsed-Field Gradient Nuclear Magnetic Resonance (PFG-NMR) [12], inverse chromatography [5], membrane permeation or modeling of the kinetics of adsorption of the solute in a batch reactor [13,14]. It is worth mentioning that PFG-NMR measures a self-diffusion coefficient, and the measurement is done only in the part of the pore space that is accessible by the probe molecule.…”